Yep, the 5/16" is a little on the small size. And yes, you'll have to do the whole thing, from inside the tank to the pump...If you go with a mechanical pump, dont get a high pressure pump, just a high volume if needed. With the high pressure, you'll need a regulator, they're over 7 # pressure...the standard ones are OK to run without a regulator. I would look at the Carter pumps before Holley...just my opinion. John